Handtrucks are widely used for carrying substantial loads. Conventional handtrucks typically include a frame having vertical posts with handles and a pair of skids or a platform extending forwardly of the posts at a right angle thereto. A pair of wheels arc mounted on either side of the handtruck proximate the intersection of the upright posts and the skids or platform. Although this design of handtruck is highly beneficial for lifting and transporting heavy articles, it still requires a significant amount of work on behalf of the operator who must provide all of the motive force.
To assist the operator in moving handtrucks as described above, a motorized handtruck has been invented and is disclosed in U.S. Pat. No. 3,205,963 to C. D. Tinker. The motorized handtruck disclosed in the Tinker patent includes a conventional handtruck further including a pair of substantially horizontally disposed base struts and a pair of substantially vertically disposed support struts. A second pair of wheels is mounted on an axle which extends between the base struts. The base struts support the driving wheels, the motor, the transmission, the driving connections between the motor and the transmission, and the driving connections between the transmission and the driving wheels. Thus, substantially the entire drivetrain is supported by the base struts which extend outwardly behind the vertical posts of the handtruck frame. As a result, the mass of the motor is disposed a substantial distance from the axle of the front wheels (i.e., the pivot fulcrum), thereby requiring great effort to tilt the motorized handtruck forward to lift the rear wheels off of the ground and/or place the handtruck in an upright position.
Another drawback of the motorized handtruck design disclosed in the patent to Tinker lies in the configuration of the base struts and the supporting struts and their relation to the driven and non-driven wheels. The configuration as disclosed does not provide for good resistance to deflection of the handtruck under load. Also, the driven wheels are not rigidly secured to the frame and the assembly is therefore not as sturdy as a given task may require. Further, the components forming the motorized portions of the handtruck are not easily adaptable for mounting on a variety of handtrucks.
Thus, there exists a need for a self-propelled handtruck which reduces the effort required to tilt the handtruck forward and/or place the handtruck in an upright position. Moreover, there exists a need for such a self-propelled handtruck which provides secure resistance to deflection due to loads when the handtruck is in a tilted, operative position. A need exists for a self-propelled handtruck providing for convenient adjustment of the handtruck's center of gravity. Finally, there exists a need for an assembly for motorizing a handtruck which is easily, conveniently, and cost effectively adaptable for and installable on a variety of conventional handtrucks.